Heretofore, a vehicle having a smart (advanced) keyless function has been known. This type of vehicle is configured such that a user who carries an electronic key can cause a desired processing to be executed in the vehicle, simply by performing a given manipulation. For example, through the use of the smart keyless function, the user can automatically unlock a door of a vehicle simply by touching a sensor provided on a door knob (or by pushing a switch provided on the door) and then automatically lock the door simply by manipulating a manipulation section provided on the vehicle when closing the door, and can start an engine simply by pushing an engine switch.
In order to fulfill such a smart keyless function, a vehicle-mounted device mounted to a vehicle and an electronic key carried by a user are configured to be triggered by each of the above manipulations to execute a given communication processing therebetween. Then, if this communication processing (i.e., authentication) is successfully completed, a given processing will be executed in the vehicle.
Typically, in the communication processing, a first communicable distance of the electronic key with respect to the vehicle-mounted device is relatively long (e.g., several tens of meters or more), whereas a second communicable distance of the vehicle-mounted device with respect to the electronic key is relatively short (e.g., about 1 m). Therefore, the smart keyless function can be effectively enabled when a user who carries the electronic key moves close to or stays within the vehicle. That is, in a situation where the user (i.e., the electronic key) is located at a position away from the vehicle by a distance greater than the second communicable distance which is about 1 m, the door of the vehicle is never unlocked, for example, even if a third party touches the sensor of the door knob.
However, in recent years, the presence of a new modus operandi for vehicle theft, called “relay attack”, has been revealed. This modus operandi comprises amplifying a communication radio wave by a relay (repeater) so that the communication processing can be successfully completed between the electronic key and the vehicle-mounted device even when they are far apart from each other, thereby enabling the smart keyless function. With to the aim of preventing vehicle theft using the relay attack, there has been proposed, as a countermeasure against the relay attack, a technique of deactivating the smart keyless function based on a user's own will (See, for example, Patent Document 1). In the technique described in the Patent Document 1, the user can temporarily deactivate the smart key function, for example, by performing a specific deactivation manipulation, using the electronic key.